bug symfony#8849 Add constructor call to the "Getting Services from the Service Container" section (viion)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes symfony#8849).

Discussion
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Add constructor call to the "Getting Services from the Service Container" section

Parent constructor call is required when using auto-wired services in a command constructor, without it you will receive the error:

```
There are no commands defined in the "app" namespace.
```

Some discussion of what I ran into: symfony#8843

Commits
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88fd7a7 Update console.rst

Author: weaverryan

console.rst

@@ -184,6 +184,8 @@ as a service, you can use normal dependency injection. Imagine you have a
         public function __construct(UserManager $userManager)
         {
             $this->userManager = $userManager;
+            
+            parent::__construct();
         }
 
         // ...